Save my goldfish....please!

Question
Hi Chris,
I have a 15lt tank, 1 goldfish, 1 smaller feeder fish and 2 littler fish (I think zebra fish?). We had a bad run recently with our goldfish dying so got the water tested, got it right, bought new fish, within 2 days the first died and now after about 2 weeks my goldfish is dying. I do a 1/2 water change every week, they dont seem to be overeating, they do all seem to be dying in the same way. They slow down in activity, then they drift, in a vertical position alot. Finally they rest in a vertical position at the bottom of the tank, with their head touching the gravel. Then they float to the top and thats it. The two little zebra ones have been alive for almost 1 year.....I understand they are pretty hardy, but all others seem to eventually go the same way. Can you help please??? I really would like to save this one!!! Thanks, Joanne.

Answer
Hi Joanne;

That's too bad. I'm so sorry you have been misled about what your goldfish need. The tank is just way too small for them, even just one alone without the danios. Each goldfish needs a minimum of 40 liters of water per fish with good filtration for high oxygen levels and waste control. For two goldfish you need at least 80 liters of water. The danios can live in very low oxygen water and are indeed very hardy. That's why they have been able to tolerate the low oxygen levels and survive every time. Here is a web page about goldfish and their needs;

http://www.firsttankguide.net/goldfish.php

At Your Service;
Chris Robbins